WASM+simd128 codegen of `a.simd_eq(Simd::splat(b)).any()` deteriorates as width increases

[alion02]

The compiler lowers the following code to a 200+ instruction long scalar sequence on WASM+simd128:

#![feature(portable_simd)]
use core::simd::prelude::*;

fn f(a: u16x32, b: u16) -> bool {
    a.simd_eq(Simd::splat(b)).any()
}

The 256-bit wide version could also arguably use some work (for example could be compiled like this), but it's not catastrophically heavy and I don't really have any benchmarks to claim that it's slow.

Meta

rustc --version --verbose:

rustc 1.78.0-nightly (c67326b06 2024-03-15)
binary: rustc
commit-hash: c67326b063bd27ed04f306ba2e372cd92e0a8751
commit-date: 2024-03-15
host: x86_64-unknown-linux-gnu
release: 1.78.0-nightly
LLVM version: 18.1.0
Compiler returned: 0

[rustbot]

Error: Label PG-portable-simd can only be set by Rust team members

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[alion02]

@rustbot modify labels: -C-bug +C-optimization +A-codegen +A-simd +A-LLVM +I-slow +I-heavy +O-wasm +requires-nightly